Chapter 51

Question 1

What structures are involved in visual stimulus tranmission from the retina to the occipital lobe?

Answer 1

optic nerve–> optic chiasm (nasal fibers cross)–> optic tracts–> LGB of thalamus–> optic radiation–> primary visual cortex

Question 2

through what stucture in the optic radiation does the lower visual field pzss?

Answer 2

Baum’s loop

Question 3

Which structure in the optic radiation cairies information from the upper visual field?

Answer 3

Meyer’s loop

Question 4

How many layers does the LGB have?

Answer 4

6

Question 5

Which LGB layers recieve input from the lateral half of the ipsilateral eye?

Answer 5

-layers II, III, V

Question 6

Where do layers I, IV, and VI recieve their fibers from?

Answer 6

-The medial half of the opposite eye

Question 7

Wha are the two principle functions of the LGB?

Answer 7

1. relay visual information from the optic tract to the visual cortex through the optic radiation
2. Gate the transmission of signals to the cortex

Question 8

What are the pinciple cells sending information to Layers I and II of the LGB?

Answer 8

• Magnocellular layer
• Information from the Large Type Y retinal ganglion cells

Remember Type Y are large visual fields and do not have high acutiy–> direct the brain to changes in the visual field

Question 9

What are the principle cells sending information to layers III, IV, V, and VI?

Answer 9

• Parvocellular layers
• Mostly type X retinal ganglion cells which are responsible for high visual acuity and color vision with medium conductance velocity

Question 10

Which of the visual areas is located at the furthest posterior part of the occipital lobe?

Answer 10

The macular vision

Question 11

What is the function of the primary visual cortex?

Answer 11

-terminus of direct visual signals from the eyes

Question 12

What is the function of the secondary visual cortex?

Answer 12

-Analysis of visual meanings

Question 13

How does the primary visual cortex interpret contrast?

Answer 13

• Equally stimulated adjacent retinal receptors mutually inhibit one another
• at borders or edges there where there is a change from dark to light or light to dark, mutual inhibition does not occur

**areas of maximum excitation occur along the sharp borders of the visual pattern

Question 14

How does determination of orientation occur in the visual cortex?

Answer 14

-result of linear organizations of mutually inhibiting cells

Question 15

How does the visual cortex determine displacement?

Answer 15

• even if an object is displaced laterally or vertically moderate distances, the same few neurons will be stimulated if the line has the same orientation
• becuase the layer IV neurons responsible are not position specific

Question 16

How is length or angle determined by the visual cortex?

Answer 16

-some neurons are stimulated only by lines or borders of specific lengths, angulated shapes, or other characteristics

Question 17

What are the two types of fixation?

Answer 17

• Voluntary- move to
• Involuntary- hold there

Question 18

Where is the primary control center for voluntary fixation? What happens if it is damaged?

Answer 18

• Frontal lobe
• difficult to unlock a fixation and move to another object or point

Question 19

Where is the primary control center for involuntary fixation? What happens if there is a lesion there?

Answer 19

-fixation can not be maintained

Question 20

If i am sitting in the car watching trees go by, what kind of mechanism am I using?

Answer 20

-Saccadic

Question 21

What is saccadic movement?

Answer 21

• Eyes jumping from one point to anther, same as in reading.
• Jumps are called Saccades, movements are called opticokinetic movements

Question 22

What is pursuit movement?

Answer 22

-when the eyes fix on a moveing object

Question 23

How does the superior colliculus contribute to fixation?

Answer 23

-SC contains a crude map of the visual field and in the event of a flash of light or disturbing stimulus, the SC sends signals to the oculomotor nerve to turn the eyes to that point in space

Question 24

How does the SC assist in movement of the head during stimulation?

Answer 24

-when a disturbance is detected in the visual field, the signals are relayed from the SC through the medial longitudinal fasciculus to other levels of the brain stem causing movement of the head and body

Question 25

How do two images from the eyes fise to form one perceivable image?

Answer 25

-images fuse with eachother on corresponding points on the two retinas–> basically managaed by parallel visual cortex

Question 26

How are neurons arranged to allow for stereopsis?

Answer 26

• some fiber pathways from the retinas to the visual cortex stray a few degrees
• different pathways are “in register” with an object a different distances

Question 27

What is strabismus? How does the body cope?

Answer 27

• Squint or cross eyed
• the body either alternates fixation with one eye and then the next, or represses the information from one eye all together and never uses it for precise vision

Question 28

What are the three componenets to the near triad?

Answer 28

• accommodation
• convergence
• miosis

Question 29

What is the neuron arc involved in the pupillary light reflex?

Answer 29

Light–> fovea–> pre-tectal nuclei–> EWN–> parasympathetics of CNIII